Managing data inconsistencies in storage systems

ABSTRACT

A method is used in managing data inconsistencies in storage systems. A data inconsistency is detected in a portion of a file system. The portion of the file system includes a set of file system data blocks. The portion of the file system is recovered. The portion of the file system is validated by using information stored in a set of mapping pointers associated with the set of file system data blocks.

CROSS REFERENCE TO OTHER APPLICATIONS

This application is continuation-in-part of and claims priority toco-pending U.S. patent application Ser. No. 14/231,075 entitledRECOVERING FROM METADATA INCONSISTENCIES IN STORAGE SYSTEMS, filed onMar. 31, 2014, which is incorporated herein by reference for allpurposes.

BACKGROUND

1. Technical Field

This application relates to managing data inconsistencies in storagesystems.

2. Description of Related Art

Computer systems may include different resources used by one or morehost processors. Resources and host processors in a computer system maybe interconnected by one or more communication connections. Theseresources may include, for example, data storage devices such as thoseincluded in the data storage systems manufactured by EMC Corporation.These data storage systems may be coupled to one or more servers or hostprocessors and provide storage services to each host processor. Multipledata storage systems from one or more different vendors may be connectedand may provide common data storage for one or more host processors in acomputer system.

A host processor may perform a variety of data processing tasks andoperations using the data storage system. For example, a host processormay perform basic system I/O operations in connection with datarequests, such as data read and write operations.

Host processor systems may store and retrieve data using a storagedevice containing a plurality of host interface units, disk drives, anddisk interface units. The host systems access the storage device througha plurality of channels provided therewith. Host systems provide dataand access control information through the channels to the storagedevice and the storage device provides data to the host systems alsothrough the channels. The host systems do not address the disk drives ofthe storage device directly, but rather, access what appears to the hostsystems as a plurality of logical disk units. The logical disk units mayor may not correspond to the actual disk drives. Allowing multiple hostsystems to access the single storage device unit allows the host systemsto share data in the device. In order to facilitate sharing of the dataon the device, additional software on the data storage systems may alsobe used.

Such a data storage system typically includes processing circuitry and aset of disk drives (disk drives are also referred to herein as simply“disks” or “drives”). In general, the processing circuitry performs loadand store operations on the set of disk drives on behalf of the hostdevices. In certain data storage systems, the disk drives of the datastorage system are distributed among one or more separate disk driveenclosures (disk drive enclosures are also referred to herein as “diskarrays” or “storage arrays”) and processing circuitry serves as afront-end to the disk drive enclosures. The processing circuitrypresents the disk drive enclosures to the host device as a single,logical storage location and allows the host device to access the diskdrives such that the individual disk drives and disk drive enclosuresare transparent to the host device.

Disk arrays are typically used to provide storage space for one or morecomputer file systems, databases, applications, and the like. For thisand other reasons, it is common for disk arrays to be structured intological partitions of storage space, called logical units (also referredto herein as LUs or LUNs). For example, at LUN creation time, storagesystem may allocate storage space of various storage devices in a diskarray to be presented as a logical volume for use by an external hostdevice. This allows a disk array to appear as a collection of separatefile systems, network drives, and/or volumes.

Disk arrays may also include groups of physical disks that are logicallybound together to represent contiguous data storage space forapplications. For example, disk arrays may be divided into redundantarray of inexpensive disks (RAID) groups, which are disk arrays createdby logically binding individual physical disks together to form the RAIDgroups. RAID groups represent a logically contiguous address spacedistributed across a set of physical disks. Each physical disk issubdivided into pieces used to spread the address space of the RAIDgroup across the group (along with parity information if applicable tothe RAID level). The physically contiguous pieces of the physical disksthat are joined together to create the logically contiguous addressspace of the RAID group are called stripes. Stripes may form blocks andblocks may be allocated to create logical representations of storagespace for use by applications within a data storage system.

As described above, applications access and store data incrementally byuse of logical storage array partitions, known as logical units (LUNs).LUNs are made up of collections of storage blocks of a RAID array andare exported from the RAID array for use at the application level.

Existing data storage systems may utilize different techniques inconnection with managing data availability in data storage systems, forexample, in the event of a data storage device failure. There are anumber of different RAID (Redundant Array of Independent or InexpensiveDisks) levels and techniques that may be used in connection withproviding a combination of fault tolerance and/or improved performancefor data storage devices. Different RAID levels (e.g., RAID-1, RAID-5,RAID-6, and the like) may provide varying degrees of fault tolerance.Further, RAID parity schemes may be utilized to provide error detectionduring the transfer and retrieval of data across a storage system.

Large storage arrays today manage many disks that are not identical.Storage arrays use different types of disks, i.e., disks with differentRAID (Redundant Array of Independent or Inexpensive Disks) levels,performance and cost characteristics.

Generally, a RAID system is an array of multiple disk drives whichappears as a single drive to a data storage system. A goal of a RAIDsystem is to spread, or stripe, a piece of data uniformly across disks(typically in units called chunks), so that a large request can beserved by multiple disks in parallel. For example, RAID-5 techniques canbe used in connection with a data storage system to protect from asingle device failure.

In a particular RAID-5 context, for example, which comprises a storagearray of five disk modules, each disk has a plurality of “N” datastorage sectors, corresponding sectors in each of the five disks beingusually referred to as a “stripe” of sectors. With respect to anystripe, 80% of the sector regions in the stripe (i.e., in a 5 disk arrayeffectively 4 out of 5 sectors) is used for user data and 20% thereof(i.e., effectively 1 out of 5 sectors) is used for redundant, or parity,data. The use of such redundancy allows for the reconstruction of userdata in the event of a failure of a user data sector in the stripe.

When a user data disk module fails, the redundant or parity entry thatis available in the parity sector of a stripe and the data in thenon-failed user data sectors of the stripe can be used to permit theuser data that was in the sector of the failed disk to be effectivelyreconstructed so that the system can remain operative using suchreconstructed data even when the user data of that sector of the faileddisk cannot be accessed. The system is then said to be operating in a“degraded” mode since extra processing operations and, accordingly,extra time is required to reconstruct the data in the failed disk sectorwhen access thereto is required.

Certain kinds of failures, however, can occur in which the storage arrayis left in an incoherent or effectively unusable state, e.g., asituation can occur in which there is power failure, i.e., power to astorage processor fails or the storage processor itself fails due to ahardware or software defect, or power to the disk drives themselvesfails.

In data storage systems where high-availability is a necessity, systemadministrators are constantly faced with the challenges of preservingdata integrity and ensuring availability of critical system components.One critical system component in any computer processing system is itsfile system. File systems include software programs and data structuresthat define the use of underlying data storage devices. File systems areresponsible for organizing disk storage into files and directories andkeeping track of which part of disk storage belong to which file andwhich are not being used.

The accuracy and consistency of a file system is necessary to relateapplications and data used by those applications. However, there mayexist the potential for data corruption in any computer system andtherefore measures are taken to periodically ensure that the file systemis consistent and accurate. In a data storage system, hundreds of filesmay be created, modified, and deleted on a regular basis. Each time afile is modified, the data storage system performs a series of filesystem updates. These updates, when written to disk storage reliably,yield a consistent file system. However, a file system can developinconsistencies in several ways. Problems may result from an uncleanshutdown, if a system is shut down improperly, or when a mounted filesystem is taken offline improperly. Inconsistencies can also result fromdefective hardware or hardware failures. Additionally, inconsistenciescan also result from software errors or user errors.

Additionally, the need for high performance, high capacity informationtechnology systems are driven by several factors. In many industries,critical information technology applications require outstanding levelsof service. At the same time, the world is experiencing an informationexplosion as more and more users demand timely access to a huge andsteadily growing mass of data including high quality multimedia content.The users also demand that information technology solutions protect dataand perform under harsh conditions with minimal data loss and minimumdata unavailability. Computing systems of all types are not onlyaccommodating more data but are also becoming more and moreinterconnected, raising the amounts of data exchanged at a geometricrate.

To address this demand, modern data storage systems (“storage systems”)are put to a variety of commercial uses. For example, they are coupledwith host systems to store data for purposes of product development, andlarge storage systems are used by financial institutions to storecritical data in large databases. For many uses to which such storagesystems are put, it is highly important that they be highly reliable andhighly efficient so that critical data is not lost or unavailable.

SUMMARY OF THE INVENTION

A method is used in managing data inconsistencies in storage systems. Adata inconsistency is detected in a portion of a file system. Theportion of the file system includes a set of file system data blocks.The portion of the file system is recovered. The portion of the filesystem is validated by using information stored in a set of mappingpointers associated with the set of file system data blocks.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the present technique will become moreapparent from the following detailed description of exemplaryembodiments thereof taken in conjunction with the accompanying drawingsin which:

FIGS. 1-2 are examples of an embodiment of a computer system that mayutilize the techniques described herein;

FIGS. 3-4 are block diagrams illustrating in more detail components thatmay be used in connection with techniques herein;

FIG. 5 is an example illustrating a storage device layout;

FIG. 6 is a block diagram illustrating in more detail components thatmay be used in connection with techniques herein;

FIGS. 7-8 are block diagrams illustrating components that may be used ina conventional system using a convention technique;

FIGS. 9-10 are block diagrams illustrating in more detail componentsthat may be used in connection with techniques herein; and

FIG. 11 is a flow diagram illustrating processes that may be used inconnection with techniques herein.

DETAILED DESCRIPTION OF EMBODIMENT(S)

Described below is a technique for use in managing data inconsistenciesin storage systems, which technique may be used to provide, among otherthings, detecting a data inconsistency in a portion of a file system,wherein the portion of the file system includes a set of file systemdata blocks, recovering the portion of the file system, and validatingthe portion of the file system by using information stored in a set ofmapping pointers associated with the set of file system data blocks.

File systems typically include metadata describing attributes of a filesystem and data from a user of the file system. A file system contains arange of file system blocks that store metadata and data. A user of afile system access the file system using a logical address (a relativeoffset in a file) and the file system converts the logical address to aphysical address of a disk storage that stores the file system. Further,a user of a data storage system creates one or more files in a filesystem. Every file includes an index node (also referred to simply as“inode”) that contains the metadata (such as permissions, ownerships,timestamps) about that file. The contents of a file are stored in acollection of data blocks. An inode of a file defines an address mapthat converts a logical address of the file to a physical address of thefile. Further, in order to create the address map, the inode includesdirect data block pointers and indirect block pointers. A data blockpointer points to a data block of a file system that contains user data.An indirect block pointer points to an indirect block that contains anarray of block pointers (to either other indirect blocks or to datablocks). There may be many levels of indirect blocks arranged in ahierarchy depending upon the size of a file where each level of indirectblocks includes pointers to indirect blocks at the next lower level.

A file is uniquely identified by a file system identification number.Each data block of a file is referenced by a logical block number and/orfile system block number. A logical block number of a file refers to adata block by relative position of the data block inside the file. Afile system block number of a file refers to a data block by relativeposition of the data block on a physical disk device on which the fileis stored. A file system block number for a data block is computed basedon a file offset and the size of the data block. Further, as describedabove herein, an inode of a file includes metadata that provides amapping to convert a file system block number of a data block to itscorresponding logical block number. For example, in case of a data blocksize of 4 kilobytes (KB), if a file offset value is smaller than 4096bytes, the file offset corresponds to the first data block of the file,which has file block number 0. Further, for example, if a file offsetvalue is equal to or greater than 4096 bytes and less than 8192 bytes,the file offset corresponds to the second data block of the file, whichhas file block number 1.

Generally, each file system data block of a file is associated with arespective mapping pointer. A mapping pointer of a file system blockpoints to the file system block and includes metadata information forthe file system block. A file system block associated with a mappingpointer may be a data block or an indirect data block which in turnpoints to other data blocks or indirect blocks. A mapping pointerincludes information that help map a logical offset of a file systemblock to a corresponding physical block address of the file systemblock.

Generally, in typical file systems, inodes, which include the metadatafor a file, are stored alongside the data that comprises the content ofthe file in a physical storage media (e.g. disks) in a data storagesystem. As such, physical storage devices store both the data itself andthe file system metadata that is related to it. Further, each filesystem block of a file of a file system is associated with a per blockmetadata (also referred to herein as “BMD”) that stores metadata for thefile system block and maintains information regarding the file systemblock such as the logical offset at which the file system block has beenallocated and so on. Further, metadata of a file system may includeinodes and indirect blocks.

The loss or corruption of any of numerous types of metadata in a systemsuch as that described above can result in inconsistencies or corruptionof a file system. For example, assume that metadata within one or morecylinders that keeps track of which blocks of storage or inodes are freeand which are allocated is corrupted or lost. Without such metadata, thefile system is unable to write additional files, as a determinationneeds to be made to identify a free inode structure and a sufficientnumber of free data blocks. As another example, if the metadata for aparticular inode is lost or corrupted, it may not be possible to accessthe corresponding file. As yet a further example, metadata in the filesystem may be corrupted so that two or more inodes both indicate thatthey own the same data block, resulting in inconsistencies regardingwhich inode actually does own the data block and has the ability tocontrol and overwrite it. It should be appreciated that such corruptionsor inconsistencies may develop in any one of numerous ways, includinghardware failures, software bugs, and so on. In addition, it should beappreciated that the types of inconsistencies and problems with the filesystems mentioned above are described merely for illustrative purposes,and that numerous other types of inconsistencies or problems arepossible.

Generally, one mechanism for recovering from corruption orinconsistencies in a storage system is to create one or more copies ofmetadata of the file system such that if the file system is unable toaccess a primary copy of the metadata, a duplicate copy of the metadatais used by the file system. Thus, a data storage system may store aduplicate copy of the inode of a file of a file system such that if thefile system is unable to access a primary copy of the inode, a duplicatecopy of the inode is used by the file system.

Generally, when a file system becomes corrupted, the file system isrecovered before the file system is subsequently accessed. In such acase, file system recovery logic evaluates metadata of the file systemand determines inconsistencies and/or errors that may have caused thecorruption of the file system. Upon detecting the inconsistencies and/orerrors in such a case, the file system recovery logic attempts torecover the file system by fixing the inconsistencies and/or errors. Inorder to recover a file system, a duplicate copy of inconsistentmetadata may be used. However, maintaining and using a duplicate copy ofmetadata consumes a large amount of system resources thereby impactingperformance of a storage system.

Further, if a storage system does not maintain a duplicate copy of filesystem metadata by turning off a feature of metadata duplication, achecksum value of metadata may be evaluated to determine whether filesystem metadata is valid. Thus, when file system data is read, a newchecksum is computed based on the file system data read and is comparedwith a checksum value associated with the file system metadata. If thenewly computed checksum does not match with the checksum value storedfor the file system data, the file system becomes offline andinaccessible to user. Further, in such a case, a file system checkutility (FSCK) attempts to recover the file system. Consequently, insuch a case, if a FSCK utility is unable to recover a file, a user maylose a large portion of enterprise data thereby causing a data loss orunavailability of the enterprise data.

Further, typically, data may be read from a single drive of a RAIDgroup. Further, data organized on a drive includes a consistency checkfor determining integrity of the data. When data is found to beinconsistent, the data is rebuilt from other drives of the RAID group.In such a case, when a write to a drive is lost and data residing on thedrive is not consistent with the data stored in an upper layer (e.g.,file system mapping layer), the consistency check for a RAID group doesnot detect the inconsistency between the upper and lower layercomponents because the data in itself is consistent even though notup-to-date between the two components.

Thus, in such a system, if file system data appears to be consistent ata RAID level when the data is read from a single drive but an upperlayer determines that the file system data is inconsistent, the upperlayer sends a request to the RAID level to rebuild the file system data.Thus, in such a case, data may be read from a single drive and is onlyrebuild upon detecting inconsistency by an upper layer.

Thus, when a file system management layer detects that a file systemblock of a file system is inconsistent, the file system management layersends a request to a multi-core RAID management layer to rebuild thefile system block based on metadata information such as LUNidentification number, offset, and length provided by file systemmanagement layer to the RAID management layer. In such a case, if themulti-core RAID management layer successfully rebuilds the file systemblock, the file system management layer compares the contents of thenewly rebuild file system by the RAID management layer with the checksumassociated with the file system block. Based upon the comparison, thefile system management layer validates that the file system block hasbeen recovered successfully by the multi-core RAID management layer. Ifthe file system block is successfully validated, the newly rebuild datais used by the file system. However, if either the multi-core RAIDmanagement layer fails to rebuild the file system block or validation ofthe file system block by the file system management layer fails, eitheran error indicating the failure is propagated through multiplecomponents to a client of a file system including the file system blockor the file system may become inactive or offline. Thus, inconsistentdata may be recovered by a lower layer component (e.g., multi-core RAIDmanagement layer) and validated by an upper layer component (e.g., filesystem management layer). Thus, in such a case, the file system blockchecksum is maintained by the file system management layer and dataresiliency is provided by the RAID management layer.

Conventionally, the file system management layer retrieves file systemblock checksum information for a file system block from per-blockmetadata of the file system block as the per-block metadata includes aninternal checksum for protecting the integrity of the information storedin the file system block. Thus, in such a conventional system, in orderto validate file system blocks of a file system hierarchy of a filesystem, the file system management layer retrieves file system blockchecksum information for each file system block of the file systemhierarchy of the file system to validate contents of each file systemblock. Further, in such a conventional system, the file systemmanagement layer reads per-block metadata of each file system block ofthe file system hierarchy in order to retrieve file system blockchecksum stored in per-block metadata of each file system block.Further, in such a conventional system, if per-block metadata of a filesystem block of a file system block hierarchy is not cached in a memoryof a storage system, the file system management layer has to retrievecontents of the per-block metadata from a storage device. Consequently,in such a conventional system, performance of a file system, a storagesystem on which the file system is organized, and a host using the filesystem is impacted when per-block metadata associated with each filesystem block of a file system block hierarchy is read from a storagedevice.

By contrast, in at least some implementations in accordance with thetechnique as described herein, storing checksum value for a file systemdata block in a mapping pointer of a leaf indirect data block pointingto the file system data block instead of per-block metadata of the filesystem data block reduces or eliminates operations performed for readingcontents of the per-block metadata from a storage device each time thefile system data block is accessed for validating contents of the filesystem data block. Thus, in at least some implementations in accordancewith the current technique, for example, if a leaf indirect data blockincludes mapping pointer for 1024 file system data blocks, the need toread per-block metadata of each file system data block of the leafindirect data block is reduced or eliminated by storing checksum valuefor each file system data block in respective mapping pointers includedin the leaf indirect data block. In at least some implementations inaccordance with the technique as described herein, checksum value (alsoreferred to herein as Cyclic Redundancy Check (“CRC”)) is provided tomulti-core RAID management layer when a read request is issued as partof a mapping operation. Further, in at least some implementations inaccordance with the technique as described herein, checksum informationfor a file system block pointed to by a leaf indirect data block thatincludes a mapping pointer to point for the file system block is updatedwhen a write request updates contents of the file system block.

In at least some implementations in accordance with the currenttechnique as described herein, the use of the managing datainconsistencies in storage systems technique can provide one or more ofthe following advantages: improving efficiency of a data storage systemby efficiently recovering from data inconsistencies in file systems,improving performance of a recovery process by using checksum valuestored in a leaf indirect data block instead of reading the checksumfrom per-block metadata that may be stored on a storage device,improving CPU utilization of a storage system by reducing or eliminatingthe need to read contents of per-block metadata from a storage device,and reducing unavailability of a file system by efficiently recoveringthe file system.

Referring now to FIG. 1, shown is an example of an embodiment of acomputer system that may be used in connection with performing thetechnique or techniques described herein. The computer system 10includes one or more data storage systems 12 connected to host systems14 a-14 n through communication medium 18. The system 10 also includes amanagement system 16 connected to one or more data storage systems 12through communication medium 20. In this embodiment of the computersystem 10, the management system 16, and the N servers or hosts 14 a-14n may access the data storage systems 12, for example, in performinginput/output (I/O) operations, data requests, and other operations. Thecommunication medium 18 may be any one or more of a variety of networksor other type of communication connections as known to those skilled inthe art. Each of the communication mediums 18 and 20 may be a networkconnection, bus, and/or other type of data link, such as hardwire orother connections known in the art. For example, the communicationmedium 18 may be the Internet, an intranet, network or other wireless orother hardwired connection(s) by which the host systems 14 a-14 n mayaccess and communicate with the data storage systems 12, and may alsocommunicate with other components (not shown) that may be included inthe computer system 10. In at least one embodiment, the communicationmedium 20 may be a LAN connection and the communication medium 18 may bean iSCSI or fibre channel connection.

Each of the host systems 14 a-14 n and the data storage systems 12included in the computer system 10 may be connected to the communicationmedium 18 by any one of a variety of connections as may be provided andsupported in accordance with the type of communication medium 18.Similarly, the management system 16 may be connected to thecommunication medium 20 by any one of variety of connections inaccordance with the type of communication medium 20. The processorsincluded in the host computer systems 14 a-14 n and management system 16may be any one of a variety of proprietary or commercially availablesingle or multi-processor system, such as an Intel-based processor, orother type of commercially available processor able to support trafficin accordance with each particular embodiment and application.

It should be noted that the particular examples of the hardware andsoftware that may be included in the data storage systems 12 aredescribed herein in more detail, and may vary with each particularembodiment. Each of the host computers 14 a-14 n, the management system16 and data storage systems may all be located at the same physicalsite, or, alternatively, may also be located in different physicallocations. In connection with communication mediums 18 and 20, a varietyof different communication protocols may be used such as SCSI, FibreChannel, iSCSI, FCoE and the like. Some or all of the connections bywhich the hosts, management system, and data storage system may beconnected to their respective communication medium may pass throughother communication devices, such as a Connectrix or other switchingequipment that may exist such as a phone line, a repeater, a multiplexeror even a satellite. In at least one embodiment, the hosts maycommunicate with the data storage systems over an iSCSI or fibre channelconnection and the management system may communicate with the datastorage systems over a separate network connection using TCP/IP. Itshould be noted that although FIG. 1 illustrates communications betweenthe hosts and data storage systems being over a first connection, andcommunications between the management system and the data storagesystems being over a second different connection, an embodiment may alsouse the same connection. The particular type and number of connectionsmay vary in accordance with particulars of each embodiment.

Each of the host computer systems may perform different types of dataoperations in accordance with different types of tasks. In theembodiment of FIG. 1, any one of the host computers 14 a-14 n may issuea data request to the data storage systems 12 to perform a dataoperation. For example, an application executing on one of the hostcomputers 14 a-14 n may perform a read or write operation resulting inone or more data requests to the data storage systems 12.

The management system 16 may be used in connection with management ofthe data storage systems 12. The management system 16 may includehardware and/or software components. The management system 16 mayinclude one or more computer processors connected to one or more I/Odevices such as, for example, a display or other output device, and aninput device such as, for example, a keyboard, mouse, and the like. Adata storage system manager may, for example, view information about acurrent storage volume configuration on a display device of themanagement system 16. The manager may also configure a data storagesystem, for example, by using management software to define a logicalgrouping of logically defined devices, referred to elsewhere herein as astorage group (SG), and restrict access to the logical group.

It should be noted that although element 12 is illustrated as a singledata storage system, such as a single data storage array, element 12 mayalso represent, for example, multiple data storage arrays alone, or incombination with, other data storage devices, systems, appliances,and/or components having suitable connectivity, such as in a SAN, in anembodiment using the techniques herein. It should also be noted that anembodiment may include data storage arrays or other components from oneor more vendors. In subsequent examples illustrated the techniquesherein, reference may be made to a single data storage array by avendor, such as by EMC Corporation of Hopkinton, Mass. However, as willbe appreciated by those skilled in the art, the techniques herein areapplicable for use with other data storage arrays by other vendors andwith other components than as described herein for purposes of example.

An embodiment of the data storage systems 12 may include one or moredata storage systems. Each of the data storage systems may include oneor more data storage devices, such as disks. One or more data storagesystems may be manufactured by one or more different vendors. Each ofthe data storage systems included in 12 may be inter-connected (notshown). Additionally, the data storage systems may also be connected tothe host systems through any one or more communication connections thatmay vary with each particular embodiment and device in accordance withthe different protocols used in a particular embodiment. The type ofcommunication connection used may vary with certain system parametersand requirements, such as those related to bandwidth and throughputrequired in accordance with a rate of I/O requests as may be issued bythe host computer systems, for example, to the data storage systems 12.

It should be noted that each of the data storage systems may operatestand-alone, or may also included as part of a storage area network(SAN) that includes, for example, other components such as other datastorage systems.

Each of the data storage systems of element 12 may include a pluralityof disk devices or volumes. The particular data storage systems andexamples as described herein for purposes of illustration should not beconstrued as a limitation. Other types of commercially available datastorage systems, as well as processors and hardware controlling accessto these particular devices, may also be included in an embodiment.

Servers or host systems, such as 14 a-14 n, provide data and accesscontrol information through channels to the storage systems, and thestorage systems may also provide data to the host systems also throughthe channels. The host systems do not address the disk drives of thestorage systems directly, but rather access to data may be provided toone or more host systems from what the host systems view as a pluralityof logical devices or logical volumes. The logical volumes may or maynot correspond to the actual disk drives. For example, one or morelogical volumes may reside on a single physical disk drive. Data in asingle storage system may be accessed by multiple hosts allowing thehosts to share the data residing therein. A LUN (logical unit number)may be used to refer to one of the foregoing logically defined devicesor volumes. An address map kept by the storage array may associate hostsystem logical address with physical device address.

In such an embodiment in which element 12 of FIG. 1 is implemented usingone or more data storage systems, each of the data storage systems mayinclude code thereon for performing the techniques as described herein.In following paragraphs, reference may be made to a particularembodiment such as, for example, an embodiment in which element 12 ofFIG. 1 includes a single data storage system, multiple data storagesystems, a data storage system having multiple storage processors, andthe like. However, it will be appreciated by those skilled in the artthat this is for purposes of illustration and should not be construed asa limitation of the techniques herein. As will be appreciated by thoseskilled in the art, the data storage system 12 may also include othercomponents than as described for purposes of illustrating the techniquesherein.

The data storage system 12 may include any one or more different typesof disk devices such as, for example, an ATA disk drive, FC disk drive,and the like. Thus, the storage system may be made up of physicaldevices with different physical and performance characteristics (e.g.,types of physical devices, disk speed such as in RPMs), RAID levels andconfigurations, allocation of cache, processors used to service an I/Orequest, and the like.

In certain cases, an enterprise can utilize different types of storagesystems to form a complete data storage environment. In one arrangement,the enterprise can utilize both a block based storage system and a filebased storage hardware, such as a VNX™ or VNXe™ system (produced by EMCCorporation, Hopkinton, Mass.). In such an arrangement, typically thefile based storage hardware operates as a front-end to the block basedstorage system such that the file based storage hardware and the blockbased storage system form a unified storage system.

Referring now to FIG. 2, shown is an example of an embodiment of acomputer system such as a unified data storage system that may be usedin connection with performing the technique or techniques describedherein. As shown, the unified data storage system 10 includes a blockbased storage system 12 and file based storage hardware 34. While theblock based storage system 12 may be configured in a variety of ways, inat least one embodiment, the block based storage system 12 is configuredas a storage area network (SAN), such as a VNX™ or VNXe™ system, asproduced by EMC Corporation of Hopkinton, Mass. While the file basedstorage hardware 34 may be configured in a variety of ways, in at leastone embodiment, the file based storage hardware 34 is configured as anetwork attached storage (NAS) system, such as a file server systemproduced by EMC Corporation of Hopkinton, Mass., configured as a headerto the block based storage system 12.

The computer system 10 includes one or more block based data storagesystems 12 connected to host systems 14 a-14 n through communicationmedium 18. The system 10 also includes a management system 16 connectedto one or more block based data storage systems 12 through communicationmedium 20. In this embodiment of the computer system 10, the managementsystem 16, and the N servers or hosts 14 a-14 n may access the blockbased data storage systems 12, for example, in performing input/output(I/O) operations, data requests, and other operations. The communicationmedium 18 may be any one or more of a variety of networks or other typeof communication connections as known to those skilled in the art. Eachof the communication mediums 18 and 20 may be a network connection, bus,and/or other type of data link, such as a hardwire or other connectionsknown in the art. For example, the communication medium 18 may be theInternet, an intranet, network or other wireless or other hardwiredconnection(s) by which the host systems 14 a-14 n may access andcommunicate with the block based data storage systems 12, and may alsocommunicate with other components (not shown) that may be included inthe computer system 10. In one embodiment, the communication medium 20may be a LAN connection and the communication medium 18 may be an iSCSIor fibre channel connection.

Each of the host systems 14 a-14 n and the block based data storagesystems 12 included in the computer system 10 may be connected to thecommunication medium 18 by any one of a variety of connections as may beprovided and supported in accordance with the type of communicationmedium 18. Similarly, the management system 16 may be connected to thecommunication medium 20 by any one of variety of connections inaccordance with the type of communication medium 20. The processorsincluded in the host computer systems 14 a-14 n and management system 16may be any one of a variety of proprietary or commercially availablesingle or multiprocessor system, such as an Intel-based processor, orother type of commercially available processor able to support trafficin accordance with each particular embodiment and application.

In at least one embodiment of the current technique, block based datastorage system 12 includes multiple storage devices 40, which aretypically hard disk drives, but which may be tape drives, flash memory,flash drives, other solid state drives, or some combination of theabove. In at least one embodiment, the storage devices may be organizedinto multiple shelves 44, each shelf containing multiple devices. In theembodiment illustrated in FIG. 1, block based data storage system 12includes two shelves, Shelf1 44A and Shelf2 44B; Shelf1 44A containseight storage devices, D1-D8, and Shelf2 also contains eight storagedevices, D9-D16.

Block based data storage system 12 may include one or more storageprocessors 46, for handling input/output (I/O) requests and allocations.Each storage processor 46 may communicate with storage devices 40through one or more data buses 48. In at least one embodiment, blockbased data storage system 12 contains two storage processors, SP1 46A,and SP2 46B, and each storage processor 46 has a dedicated data bus 48for each shelf 44. For example, SP1 46A is connected to each storagedevice 40 on Shelf1 44A via a first data bus 48A and to each storagedevice 40 on Shelf2 44B via a second data bus 48B. SP2 46B is connectedto each storage device 40 on Shelf1 44A via a third data bus 48C and toeach storage device 40 on Shelf2 44B via a fourth data bus 48D. In thismanner, each device 40 is configured to be connected to two separatedata buses 48, one to each storage processor 46. For example, storagedevices D1-D8 may be connected to data buses 48A and 48C, while storagedevices D9-D16 may be connected to data buses 48B and 48D. Thus, eachdevice 40 is connected via some data bus to both SP1 46A and SP2 46B.The configuration of block based data storage system 12, as illustratedin FIG. 2, is for illustrative purposes only, and is not considered alimitation of the current technique described herein.

In addition to the physical configuration, storage devices 40 may alsobe logically configured. For example, multiple storage devices 40 may beorganized into redundant array of inexpensive disks (RAID) groups.Although RAID groups are composed of multiple storage devices, a RAIDgroup may be conceptually treated as if it were a single storage device.As used herein, the term “storage entity” may refer to either a singlestorage device or a RAID group operating as a single storage device.

Storage entities may be further sub-divided into logical units. A singleRAID group or individual storage device may contain one or more logicalunits. Each logical unit may be further subdivided into portions of alogical unit, referred to as “slices”. In the embodiment illustrated inFIG. 1, storage devices D1-D5, is sub-divided into 3 logical units, LU142A, LU2 42B, and LU3 42C. The LUs 42 may be configured to store a datafile as a set of blocks striped across the LUs 42.

The unified data storage system 10 includes a file based storagehardware 34 that includes at least one data processor 26. The dataprocessor 26, for example, may be a commodity computer. The dataprocessor 26 sends storage access requests through physical data link 36between the data processor 26 and the block based storage system 12. Thedata link 36 may be any one or more of a variety of networks or othertype of communication connections as known to those skilled in the art.The processor included in the data processor 26 may be any one of avariety of proprietary or commercially available single ormultiprocessor system, such as an Intel-based processor, or other typeof commercially available processor able to support traffic inaccordance with each particular embodiment and application. Further,file based storage hardware 34 may further include control station 30and additional data processors (such as data processor 27) sharingstorage device 40. A dual-redundant data link 32 interconnects the dataprocessors 26, 27 to the control station 30. The control station 30monitors a heartbeat signal from each of the data processors 26, 27 inorder to detect a data processor failure. If a failed data processorcannot be successfully re-booted, the control station 30 will “fenceoff” the failed data processor and re-assign or fail-over the dataprocessing responsibilities of the failed data processor to another dataprocessor of the file based storage hardware 34. The control station 30also provides certain server configuration information to the dataprocessors 26, 27. For example, the control station maintains a bootconfiguration file accessed by each data processor 26, 27 when the dataprocessor is reset.

The data processor 26 is configured as one or more computerized devices,such as file servers, that provide end user devices (not shown) withnetworked access (e.g., NFS and CIFS facilities) to storage of the blockbased storage system 12. In at least one embodiment, the control station30 is a computerized device having a controller, such as a memory andone or more processors. The control station 30 is configured to providehardware and file system management, configuration, and maintenancecapabilities to the data storage system 10. The control station 30includes boot strap operating instructions, either as stored on a localstorage device or as part of the controller that, when executed by thecontroller following connection of the data processor 26 to the blockbased storage system 12, causes the control station 30 to detect theautomated nature of a file based storage hardware installation processand access the data processor 26 over a private internal managementnetwork and execute the file based hardware installation process.

Generally, designs of block-based and file-based data storage systemsoften follow parallel paths. Further, many of the features provided byblock-based storage, such as replication, snaps, de-duplication,migration, failover, and non-disruptive upgrade, are similar to featuresprovided for file-based data storage systems. For user convenience,block-based and file-based storage systems are sometimes co-located,essentially side-by-side, to allow processing of both block-based andfile-based host IOs in a single combined system as illustrated in FIG.2. Alternatively, both block-based and file-based functionality may becombined in an unified data path architecture. The unified data patharchitecture brings together IO processing of block-based storagesystems and file-based storage systems by expressing both block-basedobjects and file-based objects in the form of files. These files areparts of an underlying, internal set of file systems, which is stored ona set of storage units served by a storage pool. Because bothblock-based objects and file-based objects are expressed as files, acommon set of services can be applied across block-based and file-basedobjects for numerous operations, such as replication, snaps,de-duplication, migration, failover, non-disruptive upgrade, and/or manyother services, as these services are performed similarly for both blockand file objects on the same underlying type of object—a file. Further,the unified data path architecture increases storage utilization byreallocating storage resources once allocated to block-based storage tofile-based storage, and vice-versa. As block-based objects (e.g., LUNs,block-based vVols, and so forth) and file-based objects (e.g., filesystems, file-based vVols, VMDKs, VHDs, and so forth) are expressed asunderlying files, storage units released by any underlying file or filescan be reused by any other underlying file or files, regardless ofwhether the files represent block-based objects or file-based objects.Additional details regarding the unified data path architecture isdescribed in U.S. patent application Ser. No. 13/828,322 for “UnifiedDataPath Architecture”, filed Mar. 14, 2013, the contents and teachingsof which are hereby incorporated by reference in their entirety.

In at least one embodiment of the current technique, the unified datapath architecture requires a file system to be hosted on a mapped LUN asa file system on a file.

Referring to FIG. 3, shown is more detailed representation of componentsthat may be included in an embodiment using the techniques herein. Withreference also to FIGS. 1-2, in a data storage system such as datastorage system 12, a storage processor provides communications betweenhost system 90 and disk drives 110. Data storage system 100 includes atleast two storage processors 106A, 106B. Storage Processor (SPA) 106Aaccesses the disk drives 110 using communication loop (e.g., SAS) FC-AL140 and storage processor (SPB) 106B accesses the disk drives 110 usingcommunication loop FC-AL 142 (e.g. SAS).

Host system 90 may not address the disk drives of the storage systemsdirectly, but rather access to data may be provided to one or more hostsystems from what the host systems view as a plurality of logicaldevices or logical volumes (“LVs” or “LUNs”). Host system 90 sends arequest to hostside logic (“hostside”) (e.g., hostside 92) to accessdata stored on logical devices. The hostside 92 sends appropriate statusback to the host system 90 in case access to data fails. The LVs may ormay not correspond to the physical disk drives. For example, one or moreLVs may reside on a single physical disk drive. Data in a single datastorage system may be accessed by multiple hosts allowing the hosts toshare the data residing therein. Regarding terminology related to astorage system, the host or host network is sometimes referred to as thefront end and from disk adapters toward the disks is sometimes referredto as the back end. A disk adapter is a component that allows diskdrives to communicate with a storage processor.

In at least some systems, for example, host 90 sends an I/O requestthrough hostside 92 to storage processor SPA 106A. Based on the I/Orequest, SPA 106A sends corresponding data requests to disk drives 110through redirector 120, data services 124, and multi core RAIDcomponent. Redirector 120 enables the data storage system to provide analternate path to a set of disk drives by redirecting I/Os from one SPto another SP. Multi core RAID component includes multi-core cache (MCC)128, multi-core fully automated storage tiering cache (MCF) 130, andmulti-core RAID (MCR) component 132 that enable the data storage systemto interact with disk drives 110. If SPA 106A fails due to an error,responsibility of communication with a set of disk drive in a RAID groupchanges from SPA 106A to SPB 106B. In such a case, I/Os from host 90 areredirected to SPB 106B. Storage Processor SPB 106B then services thoseI/Os by sending the I/O requests to disk drives 110 through redirector122, data services 124, and multi core RAID component which includes MCC134, MCF 136 and MCR 138. In at least one embodiment of the currenttechnique, MCC 128, 134 provides a persistent cache for mirroring writedata. MCF 130, 136 reorders the I/O flow to improve system I/Operformance and response time. MCR 132, 136 leverages RAID group logicto provide management and access to disk drives 110.

Referring to FIG. 4, shown is more detailed example of an embodiment ofa computer system that may be used in connection with performing thetechniques described herein. With reference also to FIGS. 1-3, in a datastorage system such as data storage system 12, a storage processorprovides communications between host 14 and disk drives 60. Data storagesystem 12 includes at least two storage processors 106A, 106B. Bothstorage processor A (SPA) 106A and storage processor B (SPB) 106Bprovides access to LUNs 105-108 built from a storage space provided bydisk drives 60. Redirector 120, 122 interacts with storage processors106A, 106B to access LUNs 105-108. The access to LUNs 105-108 isindependent of which storage processor each Flare LUN belongs to. A userof data storage system 12 allocates storage from LUNs in fixed sizedchunks. Each fixed size chunk is known as a slice. One or more slicesare grouped together to create a slice pool. Host system 14 provisionsstorage from slice pools 100 for creating mapped LUNs 81-84. A mappedLUN is a LUN that is visible to host system 14 and a user of a datastorage system. A mapped LUN may be a thin LUN (TLU) or a direct LUN(DLU). The size of a thin LUN is independent of amount of availablestorage. Typically, storage is allocated to a thin LUN when host system14 issues a write request and needs a data block to write user's data.The size of a direct LUN is dependent of amount of available storage.Typically, storage is allocated to a direct LUN at the time the directLUN is created and initialized. File system mapping driver 85 is alight-weight file system library that provides file system functionalityand allows data storage system 12 to create files within a file system.File system mapping driver 85 processes I/Os directed to metadata of afile system. Mapped LUN driver 80 processes I/Os directed to data of thefile system. Mapped LUN driver 80 also provides slices of storage fromslice pools 100 to file system mapping driver 85 for creating a filesystem. Slices of storage can be dynamically added or removed by a filesystem. When a slice is removed, the file system redistributes datastored on the slice to other slices in the file system. File systemmapping driver 85 allocates file system blocks from slices of storagefor creating files and storing metadata of a file system. In at leastsome embodiments of the current technique, size of the file system blockmay be 8 kilobyte (KB) in size. A sparse volume concatenates slices ofstorage provided to file system mapping driver 85 into a logicalcontiguous address space on which a file system is created. The sparsevolume maintains logical to physical mapping for slices of storage in aslice database for the slices that are provisioned to address space ofthe sparse volume and are in use. Further, the file system maintains abitmap for every slice of physical storage which is in use by the filesystem such that the bitmap includes information regarding the entireaddress space of the file system. A mapped LUN presents a file as a LUNto host system 11. Further, the file presents a contiguous logicaladdress space to the mapped LUN. For example, in FIG. 5, mapped LUN 81presents file 86 as a LUN to host system 11, file 86 is created in afile system 90 and file system 90 is created from sparse volume 95.Similarly, mapped LUNs 82-84 presents file 87-89 as LUNs respectively tohost system 11, files 87-89 are created in file systems 91-93respectively and file systems 91-93 are created from sparse volumes96-98 respectively. Further, sparse volumes 95-98 are created fromslices of physical storage included in slice pools 100.

Referring to FIG. 5, shown is an example representing how data storagesystem best practices may be used to form storage pools. The example 50illustrates how storage pools may be constructed from groups of physicaldevices. For example, RAID Group1 64 a may be formed from physicaldevices 60 a. The data storage system best practices of a policy mayspecify the particular disks and configuration for the type of storagepool being formed. For example, for physical devices 60 a on a firstdata storage system type when forming a storage pool, RAID-5 may be usedin a 4+1 configuration (e.g., 4 data drives and 1 parity drive). TheRAID Group 1 64 a may provide a number of data storage LUNs 62 a. Anembodiment may also utilize one or more additional logical device layerson top of the LUNs 62 a to form one or more logical device volumes 61 a.The particular additional logical device layers used, if any, may varywith the data storage system. It should be noted that there may not be a1-1 correspondence between the LUNs of 62 a and the volumes of 61 a. Ina similar manner, device volumes 61 b may be formed or configured fromphysical devices 60 b. The storage pool 1 of the example 50 illustratestwo RAID groups being used to define a single storage pool although,more generally, one or more RAID groups may be used for form a storagepool in an embodiment using RAID techniques.

The data storage system 12 may also include one or more mapped devices70-74. A mapped device (e.g., “thin logical unit”, “direct logicalunit”) presents a logical storage space to one or more applicationsrunning on a host where different portions of the logical storage spacemay or may not have corresponding physical storage space associatedtherewith. However, the mapped device is not mapped directly to physicalstorage space. Instead, portions of the mapped storage device for whichphysical storage space exists are mapped to data devices such as devicevolumes 61 a-61 b, which are logical devices that map logical storagespace of the data device to physical storage space on the physicaldevices 60 a-60 b. Thus, an access of the logical storage space of themapped device results in either a null pointer (or equivalent)indicating that no corresponding physical storage space has yet beenallocated, or results in a reference to a data device which in turnreferences the underlying physical storage space.

A disk may be a physical disk within the storage system. A LUN may be alogical unit number which is an identifier for a Logical Unit. Eachslice of data may have a mapping to the location of the physical drivewhere it starts and ends.

Referring to FIG. 6, shown is a logical representation of a LUNpresented to a host and organized as a file system that may be includedin an embodiment using the techniques herein. With reference to FIGS.1-5, a user of data storage system 12 accesses data from LUNs stored ondisk drives 60 in fixed sized chunks. Each fixed size chunk is known asa slice. One or more slices are grouped together to create a slice pool.Host system 14 provisions storage from slice pools for creating LUNs. ALUN 170 is visible to host system 14 and a user of a data storage system12. Typically, storage is allocated when host system 14 issues a writerequest and needs a data block to write user's data.

File systems typically include metadata describing attributes of a filesystem and data from a user of the file system. A file system contains arange of file system blocks that store metadata and data. A file systemmapping driver allocates file system blocks from slices of storage forcreating files and storing metadata of a file system. In at least someembodiments of the current technique, the file system block may be 8kilobyte (KB) in size. Further, a user of data storage system 12 createsfiles in a file system. The file system is organized as a hierarchy. Atthe top of the hierarchy is a hierarchy of the directories 171 in thefile system. Inodes of data files 172 depend from the file systemdirectory hierarchy 171. Indirect blocks of data files 173 depend fromthe inodes of the data files 172. Data block metadata 174 and datablocks of data files 175 depend from the inodes of data files 172 andfrom the indirect blocks of data files 173.

A file system includes one or more file system blocks. Some of the filesystem blocks are data blocks, some file system blocks may be indirectblock, as described above, or some file system blocks are free blocksthat have not yet been allocated to any file in the file system. In anindirect mapping protocol, such as the conventional indirect mappingprotocol of a UNIX-based file system, the indirect mapping protocolpermits any free block of the file system to be allocated to a file ofthe file system and mapped to any logical block of a logical extent ofthe file. This unrestricted mapping ability of the conventional indirectmapping protocol of a UNIX-based file system is a result of the factthat metadata for each file includes a respective pointer to each datablock of the file of the file system, as described below. Each file ofthe file system includes an inode containing attributes of the file anda block pointer array containing pointers to data blocks of the file.There is one inode for each file in the file system. Each inode can beidentified by an inode number. Several inodes may fit into one of thefile system blocks. The inode number can be easily translated into ablock number and an offset of the inode from the start of the block.Each inode of a file contains metadata of the file. Some block pointersof a file point directly at data blocks, other block pointers of thefile points at blocks of more pointers, known as an indirect block.There are at least fifteen block pointer entries in a block pointerarray contained in an inode of a file. The first of up to twelve entriesof block pointers in the inode directly point to the first of up totwelve data blocks of the file. If the file contains more than twelvedata blocks, then the thirteenth entry of the block pointer arraycontains an indirect block pointer pointing to an indirect blockcontaining pointers to one or more additional data blocks. If the filecontains so many data blocks that the indirect block becomes full ofblock pointers, then the fourteenth entry of the block pointer arraycontains a double indirect block pointer to an indirect block thatitself points to an indirect block that points to one or more additionaldata blocks. If the file is so large that the indirect block becomesfull of block pointers and its descendant indirect blocks are also fullof block pointers, then the fifteenth entry of the block pointer arrayincludes another level of indirection where the block pointer entrycontains a triple indirect block pointer to an indirect block thatpoints to an indirect block that points to an indirect block that pointsto one or more additional data blocks. Similarly there exists fourth andfifth level of indirections. Once the indirect blocks at last level ofindirection and its descendant indirect blocks become full of pointers,the file contains a maximum permitted number of data blocks. Further, anindirect block at the last level of indirection is also referred to as aleaf indirect block. However, it should be noted that a file system maybe organized based on any one of the known mapping techniques such as anextent based binary tree mapping mechanism.

Referring to FIG. 7, shown is a representation of a conventional perblock metadata (also referred to as “BMD”) for a file system data blockthat may be included in a conventional system using conventionaltechniques. The per-block metadata 180 for a file system data blockincludes an inode number of a file of the file system, the file systemdata block number and the logical offset 184 of the file system datablock. Conventionally, the per-block metadata 180 for a file system datablock also includes an internal checksum 183 protecting the integrity ofthe information stored in the per-block metadata 180. The per-blockmetadata for a file system data block may further include a mappingpointer and a data structure indicating state of the per-block metadata181 and total distributed weight 182 for the file system data block ifit has been shared by two or more file system blocks.

Referring to FIG. 8, shown is a representation of a conventional mappingpointer 190 of a file system data block that may be included in aconventional system using conventional techniques. Generally, each filesystem data block of a file is associated with a respective mappingpointer. A mapping pointer of a file system block points to the filesystem block and includes metadata information for the file systemblock. A file system block associated with a mapping pointer may be adata block or an indirect block which in turn points to other datablocks or indirect blocks. A mapping pointer includes information thathelp map a logical offset of a file system block to a correspondingphysical block address of the file system block. Mapping pointer 190includes metadata information such as sharing status 192, weight 191,and block address 193. Sharing status 192 of mapping pointer 190associated with a file system data block indicates whether the datablock (or data blocks if the mapping pointer is associated with anindirect block) may be shared. Weight 191 of mapping pointer 190 for afile system block indicates a delegated reference count for the mappingpointer 190. The delegated reference count is used by a snapshot copyfacility when a replica of a file is created. Mapping pointers of theinode of the file are copied and included in the inode of the replica ofthe file. Generally, mapping pointers of the inode may include mappingpointers pointing to direct data blocks and mapping pointers pointing toindirect blocks. Then, the delegated reference count values stored inthe mapping pointers of the file and the replica of the file are updatedto indicate that the file and the replica of the file share data blocksof the file. Block address 193 of mapping pointer 190 for a file systemblock indicates the block number of the file system block.Alternatively, block address 193 of mapping pointer 190 may indicate aVirtual Block Metadata (“VBM”) identification number which points to aVBM object that points to a data block and includes metadata for thedata block. Thus, a VBM object includes file system data block mappingpointer as described in FIG. 8. It also includes a total distributedweight for the VBM object which is the sum of weights of each mappingpointer for a file system block pointing to the VBM object. The VBMobject may further includes a mapping pointer which may point to a filesystem block or another VBM object such that the mapping pointerincludes the distributed weight for the mapping pointer.

Referring to FIG. 9, shown is a representation of a per block metadata(also referred to as “BMD”) for a file system data block that may beincluded in an embodiment using the current techniques described herein.In at least one embodiment of the current technique, internal checksum183 protecting the integrity of the information that has been previouslystored in a conventional per-block metadata is no longer stored in theper-block metadata 180.

Referring to FIG. 10, shown is a representation of a mapping pointer 190of a file system data block that may be included in an embodiment usingthe techniques described herein. In at least one embodiment of thecurrent technique, internal checksum 183 protecting the integrity of theinformation that has been previously stored in a conventional per-blockmetadata is now stored in mapping pointer 190 of a file system datablock included in a leaf indirect data block that points to the filesystem data block.

Referring to FIG. 11, shown is a more detailed flow diagram illustratingmanaging data inconsistencies in storage systems. With reference also toFIGS. 1-10, a data inconsistency in one or more file system block isdetected in a file system by data services 124, 126 which may includefile system mapping driver 85 (step 200). File system mapping driver 85sends a request to RAID management component such as MCR 132, 138 forrecovering from the data inconsistency by rebuilding a set of filesystem blocks that has been found to be inconsistent (step 202). Adetermination is made as to whether MCR 132, 138 has been successful inrebuilding the set of file system blocks. Upon determining thatrebuilding of contents of the set of file system blocks has beensuccessful, file system mapping driver 85 validates the newly rebuilddata by comparing checksum associated with the set of file system blockswith the newly computed checksum for the newly rebuild data (step 204).For validating newly rebuild data of a file system data block, checksumvalue stored in a mapping pointer for the file system data blockincluded in a leaf indirect data block that points to the file systemdata block is compared with newly computed checksum for the newlyrebuild data of the file system data block.

A determination is made as to whether validation of the newly rebuilddata has been successful. Upon determining that file system mappingdriver 85 has successfully validated the newly rebuild set of filesystem blocks, the newly rebuild set of file system blocks are used bythe file system mapping layer 85. However, upon determining thatvalidation of the newly rebuild set of file system blocks has failed,the file system is marked as offline for a recovery and access to thefile system is lost.

Further, in at least one embodiment of the current technique, checksumvalue stored in a mapping pointer for a file system data block includedin a leaf indirect data block that points to the file system data blockis updated when contents of the file system data block are changed uponreceiving a write request.

Generally, a file system mapping driver 85 includes a capability fordetecting data and/or metadata inconsistencies. Further, a checksumvalue is managed for each file system block to detect whether a filesystem block contains valid data. Generally, when contents of a filesystem block are read, a new checksum is computed and compared with thechecksum value associated with the file system block.

Further, it should be noted that using RAID group logic is one way forrebuilding inconsistent data and any other known method for rebuildinginconsistent data may be employed by a RAID management component.Further, it should be noted that a RAID group may employ any number ofknown parity schemes.

While the invention has been disclosed in connection with preferredembodiments shown and described in detail, their modifications andimprovements thereon will become readily apparent to those skilled inthe art. Accordingly, the spirit and scope of the present inventionshould be limited only by the following claims.

What is claimed is:
 1. A method for use in managing data inconsistencies in storage systems, the method comprising: detecting a data inconsistency in a portion of a file system, wherein the portion of the file system includes a set of file system data blocks; recovering the portion of the file system; and validating the portion of the file system by using information stored in a set of mapping pointers associated with the set of file system data blocks, wherein a file system mapping logic works in conjunction with a multi-core RAID logic for detecting the data inconsistency in the portion of the file system.
 2. The method of claim 1, wherein validating the portion of the file system further comprising: comparing a newly computed checksum for each file system data block of the set of file system data blocks and a checksum value included in a mapping pointer for each file system data block.
 3. The method of claim 1, wherein a file system is associated with a set of sparse volumes, wherein each sparse volume includes a set of slices, each slice of the set of slices is a logical representation of a subset of physical disk storage.
 4. The method of claim 1, wherein the file system resides on a storage system, wherein the storage system includes a disk drive system comprising a plurality of Redundant Array of Inexpensive Disks (RAID) systems, each RAID system of the plurality of RAID systems having a first disk drive and a second disk drive.
 5. The method of claim 1, further comprising: updating a state of the file system to an offline state for recovering the file system upon determining that the validation of the portion of the file system has failed.
 6. The method of claim 1, wherein the file system is represented by a file system hierarchy, the file system hierarchy including a set of indirect data blocks, each indirect data block including a set of data blocks.
 7. The method of claim 1, wherein each file system data block of the set of file system data blocks is associated with a mapping pointer, wherein a mapping pointer includes a checksum value for a file system data block.
 8. The method of claim 1, wherein an indirect data block includes a set of mapping pointers, wherein each mapping pointer points to a file system data block.
 9. A method for use in managing data inconsistencies in storage systems, the method comprising: detecting a data inconsistency in a portion of a file system, wherein the portion of the file system includes a set of file system data blocks; recovering the portion of the file system; and validating the portion of the file system by using information stored in a set of mapping pointers associated with the set of file system data blocks, wherein the portion of the file system is recovered by rebuilding the portion of the file system by a multi-core RAID logic.
 10. The method of claim 9, wherein each file system data block of the set of file system data blocks is associated with a mapping pointer, wherein a mapping pointer includes a checksum value for a file system data block.
 11. A system for use in managing data inconsistencies in storage systems, the system comprising a processor configured to: detect a data inconsistency in a portion of a file system, wherein the portion of the file system includes a set of file system data blocks; recover the portion of the file system; and validate the portion of the file system by using information stored in a set of mapping pointers associated with the set of file system data blocks, wherein a file system mapping logic works in conjunction with a multi-core RAID logic for detecting the data inconsistency in the portion of the file system.
 12. The system of claim 11, wherein validating the portion of the file system further comprising: comparing a newly computed checksum for each file system data block of the set of file system data blocks and a checksum value included in a mapping pointer for each file system data block.
 13. The system of claim 11, wherein a file system is associated with a set of sparse volumes, wherein each sparse volume includes a set of slices, each slice of the set of slices is a logical representation of a subset of physical disk storage.
 14. The system of claim 11, wherein the file system resides on a storage system, wherein the storage system includes a disk drive system comprising a plurality of Redundant Array of Inexpensive Disks (RAID) systems, each RAID system of the plurality of RAID systems having a first disk drive and a second disk drive.
 15. The system of claim 11, further comprising: update a state of the file system to an offline state for recovering the file system upon determining that the validation of the portion of the file system has failed.
 16. The system of claim 11, wherein the file system is represented by a file system hierarchy, the file system hierarchy including a set of indirect data blocks, each indirect data block including a set of data blocks.
 17. The system of claim 11, wherein each file system data block of the set of file system data blocks is associated with a mapping pointer, wherein a mapping pointer includes a checksum value for a file system data block.
 18. The system of claim 11, wherein an indirect data block includes a set of mapping pointers, wherein each mapping pointer points to a file system data block.
 19. A system for use in managing data inconsistencies in storage systems, the system comprising a processor configured to: detect a data inconsistency in a portion of a file system, wherein the portion of the file system includes a set of file system data blocks; recover the portion of the file system; and validate the portion of the file system by using information stored in a set of mapping pointers associated with the set of file system data blocks, wherein the portion of the file system is recovered by rebuilding the portion of the file system by a multi-core RAID logic.
 20. The system of claim 19, wherein each file system data block of the set of file system data blocks is associated with a mapping pointer, wherein a mapping pointer includes a checksum value for a file system data block. 